The effect of airflow direction and air channeling inside computer chassis

May 2010

The above diagram illustrates airflow direction for a fan in free air. So let’s take a closer look at air intake into the fan and air blowing out in two parts：
Air intake：Air follows the physics of moving from high pressure area into low pressure area so air enters the fan evenly.

Air exhaust：Due to centrifugal force and compression through the fan frame,airflow will spread outward as it leaves the fan. As a result, there will be a vacuum area absent of airflow (dead spot) that is wider than the fan hub above/beyond the center of the fan.

With the knowledge of the basic fan airflow as a guide, we can determine that using a fan as exhaust is ideal because airflow gets sucked into the fan evenly. The higher the capacity of the fan, the better it will be as an exhaust device. However, using a fan as an intake device will create dead spots so designing a case with proper intake fans is a much more difficult task. The illustration above only shows fan airflow direction in free air, but it does not explain what happens when a fan is applied as an intake device for a computer case.

From the testing that we’ve conducted, adding resistance on the intake side (such as fan filter), will cause airflow to spread more outward than in free air. Fans with lower air pressure will see the effect of airflow spreading outward even more dramatically. Bigger fans will also see bigger dead spot. Increasing fan speed to increase air pressure can help reduce airflow from spreading but this is not an optimal solution because higher fan speed increases noise.

So what happens with an intake fan inside a computer case?

Inside a computer case, the side walls of the case can contain airflow but due to the effect explained earlier, the airflow will still spread out and travel along the side wall, leaving dead spot in the middle of the case. This poor utilization of airflow results in ineffective cooling for the case.

When we designed the RAVEN RV02, we added honeycomb air guide cover that doubles as fan guard to improve airflow direction.

The honeycomb holes have equal depth and are evenly spread, this create numerous air guide to force air to travel upwards in parallel. Although the overall measured airflow rate will decrease with added air guide, the effective airflow is increased due to dramatically less dead spot area. This helps cooling performance to increase inside the case. So instead of trying to increase airflow for the fans (and increase noise), we found a way to increase airflow efficiency.

But there is an even better way to improve airflow efficiency…

By redesigning the fan grille on the fan itself, the “Air Penetrator” series fans dramatically improve airflow efficiency over traditional fans. The combination of fan blades twisting air into the swirl-shaped fan grille forces airflow to tumble forward in a circular fashion that virtually eliminates dead spot. The air penetrator’s airflow is vastly more focused, and can reach much further as well. This design is also superior to adding a honeycomb grille on a traditional fan because there is one less obstacle for air to travel through.

Air Penetrator’s fan grille is built into the fan frame and is dense enough to act as fan guard so there is no need to add another fan grille over it for protection. In the RV02 and FT02 cases, the original fan grille must be removed for them to fit 12.2 inch graphics cards over their installed fan, but this leaves fan blades exposed. With the Air Penetrator fans installed, no changes are needed to fit 12.2 inch graphics cards and there will be no concerns for exposed fan blades.

First case to be equipped with Air Penetrator fan – SG07 (fan model: AP181)

The SG07 is the newest member of the Sugo family of small form factor (SFF) cases. It is designed to accommodate Mini-ITX motherboards and the case fan used is actually bigger than the motherboard. If we were to use traditional fan, the dead spot would have covered nearly the entire motherboard and the CPU cooler (left illustration). By using the Air Penetrator (AP181) on the SG07, we can ensure all the effective airflow are being directed downward to the CPU cooler and through to the motherboard surface. This allows users to utilize coolers such as SilverStone’s own NT06-E without additional fan to support CPU with TDP ratings up to 95W and still have airflow left to cool all components on the motherboard.

We are proud to present this new product to showcase SilverStone’s continued excellence in innovation and breakthrough for improving computer thermodynamics.